1. Field of Invention
The present invention relates to an improved method for preparing oxycodone. More particularly, the present invention sets forth a method for preparing oxycodone in high yields that does not require the employment, or synthesis, of thebaine in the reaction scheme.
2. Background of the Related Art
The analgesic activity of Papaver somniferum has been known since antiquity. It has long been understood that the milky juice derived from the unripe seed capsules of this poppy plant possesses potent pharmacological properties. The dried and powdered form of the juice is referred to as opium. Opium comprises about 10% of the juice obtained from the unripe seed capsules of Papaver somniferum.
Early in the nineteenth century it was recognized that opium contains numerous alkaloid compounds. The first of these alkaloids to be isolated was morphine, described by Serturner in 1805. The isolation of other alkaloids, including codeine (Robiquet 1832), papaverine (Merck 1848), thebaine, oripavine and noscapine followed in short order. By the middle of the nineteenth century, the use of pure alkaloids rather than crude opium preparations was established medical practice. It is now known that opium contains more than twenty distinct alkaloids.
In general, the opium alkaloids can be divided into five distinct chemical classes: phenanthrene, benzylisoquinoline, tetrahydroisoquinoline, cryptopine and miscellaneous (Remington's Pharmaceutical Sciences 433, 1975). Therapeutically usefuil drugs are primarily isolated from the phenanthrene and benzylisoquinoline classes. The principal phenanthrenes are morphine (.apprxeq.10% of opium), codeine (.apprxeq.0.5% of opium) and thebaine (.apprxeq.0.2% of opium). The principal benzylisoquinolines are papaverine (.apprxeq.1.0% of opium) and noscapine (.apprxeq.6.0% of opium).
Morphine itself comprises a 5-ring structure, incorporating a partially hydrogenated phenanthrene ring system. Each ring of morphine is designated as set forth below: ##STR1##
Morphine includes what is referred to in the art as a morphinan ring structure, comprising rings A, B, C and E, as set forth below: ##STR2##
The substituent numbering of morphine derivatives follows two common conventions as shown: ##STR3##